The development of modern, industrial agriculture has been characterized by large reductions in biological diversity, both across landscapes and within farming systems. Loss of biodiversity is particularly evident in the U.S. Corn Belt, where the landscape is dominated by two commodity crops, corn and soybean, and concentrated animal feeding operations used to produce large numbers of poultry, hogs, and cattle. Iowa, in the heart of the Corn Belt, exemplifies this pattern. About 65% of Iowa's 15 million hectares of land is occupied by corn and soybean,1 with that percentage exceeding 90% in many counties.2 The state has a human population of 3.1 million, but is also home to poultry and livestock populations that produce a quantity of manure equal to that generated by 134 million people.3 Iowa ranks last nationally in the amount of pre-Euro American settlement vegetation still remaining,4 with the state’s prairie communities reduced to <0.1% of their former area.5
Simplification of crop and non-crop vegetation and concentration of animal production in the Corn Belt has resulted in large amounts of grain, alcohol, and livestock products, but also in multiple challenges, including soil erosion, water quality degradation, herbicide-resistant weeds, new crop diseases, volatility in farm profitability, and sharp declines in populations of pollinators, natural enemies of crop pests, and wildlife species.6 7 Current patterns of land use and agricultural production in the U.S. Corn Belt have had important impacts on adjacent urban areas as well. These include increased frequency of flooding and attendant property damage, increased costs of drinking water treatment, loss of recreational opportunities, and lack of access to a full spectrum of locally produced food products.8 9 10 11 Projected changes in climate for this region include increases in the proportion of precipitation coming from extreme events, which could make soil and water conservation in existing cropping systems more difficult and flood damage in urban areas more common and more severe.12
Given the loss in the Corn Belt of native biodiversity, crop diversity, and the ecosystem services that biodiversity can provide, it is appropriate to ask, "Are impoverished biological communities and environmental degradation unavoidable costs of high agricultural productivity or can land use strategies be developed to provide food security, profitable livelihoods, environmental protection, and greater resilience to climate change and other challenges?" Results of two long-term, large-scale experiments conducted in Iowa suggest that increasing biodiversity can indeed be a viable strategy for improving agroecosystem health and resilience.
Since 2007, the Science-based Trials of Row-crops Integrated with Prairie Strips (STRIPS) study has assessed the effects of integrating strips of reconstructed native prairie vegetation with corn and soybean production. This work has been conducted on a small-watershed and field scale on the Neal Smith National Wildlife Refuge in Prairie City, IA, and on more than 40 farm sites across Iowa and northern Missouri. Data from this study indicate that conversion of small amounts of cropland (<10% of a watershed) to prairie vegetation can provide disproportionately large improvements in conservation of soil, nutrients, water, and wildlife. Investigators 13 reported that compared with catchments containing only crops, integrating prairie strips into cropland led to a 2.1-fold increase in the abundance of bird species of conservation need; a 2.6-fold increase in the number of insect taxa; and a 3.5-fold increase in pollinator abundance. Additionally, the use of prairie strips reduced total water runoff from catchments by 37%, resulting in retention of 20 times more soil and 4.3 times more phosphorus. Social surveys showed that there was demand among both farm and non-farm populations for the conservation and biodiversity effects that prairie strips produced. Based on analyses conducted with the Agricultural Conservation Planning Framework,14 it has been suggested that prairie strips could be used to improve biodiversity and ecosystem services on 40% of the 9.8 million hectares of corn and soybean fields in Iowa.15
Since 2001, a 9-hectare field experiment at the Iowa State University Marsden Farm has been used to investigate how cropping system diversification and crop-livestock integration affect productivity, profitability, and environmental quality. The status quo is represented in the experiment by a conventional 2-year corn/soybean rotation, whereas more diverse systems integrated with livestock production are represented by a 3-year corn/soybean/oat + red clover rotation and a 4-year corn/soybean/oat + alfalfa/alfalfa rotation, both of which periodically receive cattle manure. Compared with the 2-year rotation, yields in the longer, more diverse rotations have averaged 4% higher for corn and 16% higher for soybean, despite 86-91% reductions in the use of mineral nitrogen fertilizer and 96-97% reductions in the use of herbicides.16 17 Three indicators of soil quality–particulate organic matter carbon, microbial biomass carbon, and potentially mineralizable nitrogen–were 22–51% higher in the 3-year and 4-year rotations than in the 2-year rotation,18 19 and incidence and severity of sudden death syndrome, a key disease affecting soybean, were markedly lower in the longer rotations.20 Spring (March-May) concentrations of nitrate in drainage water collected from corn in the more diverse systems were 57% lower than from corn in the 2-year system.21 Compared with the conventional 2-year rotation, the longer rotations exhibited reductions in fossil energy consumption,22 herbicide-related aquatic ecotoxicity,23 and discharge of soil sediment, nitrogen, and phosphorus in run-off water.24 Net annual returns to land and management did not differ between cropping systems, averaging $858 per hectare.25 Collectively, these results indicate that increasing cropping system diversity and reintegrating crop and livestock production can help meet productivity, profitability, and environmental quality goals.
It remains to be determined how adjacent urban areas would be affected by the types of cropping system diversification and land use changes explored in the aforementioned studies. One way to initiate such inquiry is with scenario development.26 In one example, investigators 27 compared four scenarios for farming practices and land use in three Iowa counties north of the city of Des Moines, based on combinations of differing economic goals (high material throughput vs. high human and environmental welfare) and differing fossil energy costs (inexpensive vs. expensive). In situations where human and environmental welfare were emphasized over high material throughput, researchers 28 suggested that the land area used for corn and soybean production would diminish and more land would be used for horticultural crops, grazing livestock, and soil, water, and wildlife conservation. As energy became expensive, they suggested that agricultural production would be concentrated near urban areas to minimize the distances that products would need to travel to reach consumers, and to reduce storage requirements. The next steps in evaluating linkages between rural land use, farming practices, and urban areas involve the use of biophysical and socioeconomic models to quantify the impacts of contrasting scenarios. Such models not yet been fully applied for mid-size cities in the U.S. Corn Belt and adjacent rural land, but could provide valuable information for planners, environmentalists, and other personnel working on rural and urban quality of life and economic development.
References cited are included in the footnotes provided below.
This event is supported by the National Science Foundation, Award #1929601. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.